This invention relates generally to heat pump systems, and in particular, to a method and apparatus for controlling the pressure within the interconnecting tubing and other refrigerant containing components thereof to prevent the maximum design pressure from being exceeded when using a high pressure refrigerant.
The refrigerant which has been commonly used in conventional residential and commercial air conditioners and heat pumps has been R-22, an HCFC refrigerant. However, because of the recent concern about environmental effects, CFC and HCFC refrigerants are being phased out. The non-chlorinated refrigerants which are being developed as replacements in the residential and light commercial systems tend to be of higher pressure than the R-22 refrigerant. One of the more promising replacement refrigerants is HFC R-410A, with operating pressures up to 70% higher than R-22.
Use of higher pressure refrigerants has the greatest impact on the high pressure side of a system. Accordingly, for an air conditioner, the outdoor unit needs to be substantially changed in design in order to accommodate these higher pressures. That is, to meet the requirements of safety agencies and organizations, most refrigerant containing components on the high pressure side of the system must be designed to withstand the significantly higher pressures. Existing low pressure side components, on the other hand, may be used with only minor modifications and/or precautions. The costs associated with these changes of both the outdoor and indoor sections of an air conditioner to accommodate an R-410A refrigerant is not significantly higher than that for replacing an R-22 air conditioner with a new R-22 air conditioner and is therefore economically feasible. This is not necessarily so in the case of a heat pump.
To accommodate an R-410A heat pump operating in the cooling mode, the outdoor section must be redesigned to accommodate the higher pressures as discussed above. In addition, to accommodate the heating mode of operation, wherein the high pressure section is in the indoor coil, the indoor refrigerant containing components, as well as other components in the outdoor unit, must be redesigned.
In addition to the outdoor and indoor coils, there is a portion of the system known as the xe2x80x9cline setxe2x80x9d which is the interconnecting tubing connecting the indoor and outdoor sections of air conditioners and heat pumps. Typically, R-22 air conditioners and heat pumps have used what is referred to as RST (Refrigerant Service Tube ) refrigeration copper tubing for line sets. The physical dimensions of RST tubing is not regulated or recognized by any safety organization or set by national standards but is simply the general air conditioning and refrigerant industry accepted tubing.
The line set is typically considered to be field fabricated and is generally regulated by local building codes. Most local and national codes for refrigerant piping reference the ASME standard, ASME B31.5 xe2x80x9cRefrigeration Piping.xe2x80x9d For R-410A air conditioners and R-410A heat pumps operating in the cooling mode, the standard RST tubing meets the requirements set forth in the ASME B31.5 standard. However, with heat pumps, the conventional R-22 construction of the line set vapor line typically does not meet the requirement of the ASME B31.5 standard. That is, a standard RST vapor tube installed in a heat pump has a rated working pressure below that of the ASME B31.5 standard when using R-410A as a refrigerant.
One approach to accommodating the R-410A refrigerant is to change the line sets or at least the vapor line. However, this causes disproportionate costs to be incurred. First of all, the line sets of existing systems are often located in the walls between the outdoor and indoor systems and cannot be easily accessed. Second, apart from the labor costs, the cost of copper tubing is expensive because (a) thicker walls require more copper, and (b) the low volume of thicker walled copper tubes drives costs up disproportionately. For these reasons, the required changes that need to be made to an R-22 heat pump to accommodate the use of R-410A are significantly higher than the cost to replace the R-22 system with a new R-410A system, so retrofitting is therefore not economically feasible.
Briefly stated, a heat pump system includes an outdoor unit, an indoor unit, a compressor, and outdoor and indoor fans. An outdoor heat exchanger coil is connected to an indoor heat exchanger coil by liquid and vapor tubes. A control system limits the pressure in the vapor tubes during heating mode periods of heat pump operation by using a temperature sensor including a switch operatively connected in the indoor heat exchanger coil for sensing a temperature in the indoor heat exchanger coil. The switch operatively connects in series with a motor of the outdoor fan, such that when the temperature sensor senses a predetermined temperature in the indoor heat exchanger coil, it causes the switch to reduce a speed of the outdoor fan, thereby reducing the temperature in the vapor tubes and indoor heat exchanger coil.
According to an embodiment of the invention, a heat pump system includes a compressor, an outdoor fan and an indoor fan, an outdoor coil and an indoor coil interconnected by liquid and vapor lines, and a reversing valve operable selectively to direct refrigerant flow for either cooling or heating modes of operation, and a control system for allowing a replacement refrigerant having a substantially higher pressure than an original refrigerant for which the system was designed, without replacement of any lines in the indoor coil or the vapor line. The heat pump system includes temperature sensing means for sensing when a temperature in the vapor lines exceeds a predetermined temperature limit during periods of operation in the heating mode; and speed reducing means for responsively reducing a speed of the outdoor fan thereby to lower the temperature to an acceptable limit below the predetermined temperature limit.
According to an embodiment of the invention, a heat pump system includes an outdoor unit with a compressor, an outdoor fan, an outdoor heat exchanger coil, an indoor heat exchanger coil connected thereto by liquid and vapor tubes, and a control system for limiting the pressure in the vapor line during periods of heat pump operation. The system includes a temperature sensor including a switch operatively connected in the indoor heat exchanger coil for sensing a temperature in the indoor heat exchanger coil; the switch being operatively connected in series with a motor of the outdoor fan; wherein when the temperature sensor senses a predetermined temperature in the indoor heat exchanger coil and causes the switch to reduce a speed of the outdoor fan, thereby reducing a temperature in the indoor heat exchanger coil.
According to an embodiment of the invention, in a heat pump of the type having a compressor, an outdoor fan, an indoor fan, an outdoor coil and an indoor coil interconnected by respective liquid and vapor interconnecting tubes, wherein a pressure in at least one of the tubes is susceptible to exceeding a predetermined maximum operating pressure during periods of operation in a heating mode, a method of controlling the pressure in the tubes includes the steps of (a) sensing a temperature in the indoor coil; comparing the sensed temperature with a predetermined maximum threshold temperature which is below a predetermined maximum temperature corresponding to the maximum design pressure; and (b) reducing a speed of the outdoor fan when the sensed temperature is equal to the maximum temperature.